Brain-eating blobs from Hell

It’s a sweltering summer’s day in outback Australia. Sweat rolls off your forehead in glistening beads, stinging your eyes and salting your tongue. The country radio blares: ‘Keep cool today, folks – we’re heading for a top of 44 degrees’. But not to worry – you’ve just stumbled upon an inviting roadside dam. A lonely gum tree shades the murky water, a tire dangling from one branch. You jump out of the car and dive into the tepid pool without a second thought. Pure bliss! Thoroughly refreshed, you hop back in the ute and speed away. A week later, you’re dead.

A much more inviting pool than the one you saw from the roadside – but probably just as deadly.Image by yaruman5, via Flickr.

Hot water means hungry zombies

If pathologists were to perform an autopsy on your corpse, they’d find nothing unusual – just a run-of-the-mill bunch of organs. That is, unless they opened up your skull. Why? Meet Naegleria fowleri – better known as the brain-eating amoeba.

This unassuming little microbe was discovered in 1965 in a South Australian children’s hospital, when a spate of fatalilities was traced back to Naegleria’s presencein unchlorinated tap water. In the decades since, infections have been reported from countries as far afield as Pakistan and the US. Unlike many of the parasites that afflict the human race, Naegleria doesn’t need a host to survive or carry out its life cycle.Naegleria spends its day-to-day life gulping up bacteria in warm freshwater pools – but when an unsuspecting human hops in for a quick splash, Naegleria sees greener pastures. Why waste energy chasing after tiny microbes when there’s a smorgasbord right in front of you?

Mind on the menu

Naegleria wants to eat your brains, but how does it get to them? Swallowing this creepy amoeba won’t lead to infection, since stomach acid would make short work of any stray Naegleria. Entering via an open wound is also fruitless: the blood-brain barrierwould comfortably block access to your grey matter, if the immune system didn’t fight off infection first. To undercut the natural defences of our body, this ingenious invader takes the road less travelled. Its strategy is nothing to sniff at: it climbs into the cranium through your nose.

When a swimmer in a Naegleria-infested pool accidentally inhales water, some of the droplets make it all the way up the nostrils – and some Naegleria come along for the ride. Nestled at the top of our nose is a structure called the cribiform plate. This plate is full of tiny holes that support our olfactory nerves; these nerves are crucial for our sense of smell and taste. They’re also the ropes Naegleria uses in its upward trek. After climbing through the cribiform plate, the tiny zombies can sense the biggest feast of their life is coming, and start to multiply.

At this point, it’s game over for the brain. The hungry amoebae whip out their feeding apparatus (a bizarre sucking structure called an amoebostome) and start to munch away. Cell by cell, the brain starts to break down. First the olfactory bulb, then the frontal lobe, and then… death. After a week of headaches, back pain and seizures, the victim draws their last breath. With nowhere else to go, the Naegleria eventually die too – but what an incredible last supper!

Naegleriasis is incredibly deadly, so it may scare you even more to know that there’s no reliable cure to fight it! Trials with antifungal drugs and whole-body cooling have saved a few patients, but the number of successes could be counted on your fingers. Most survivors also come away from the near-death experience with permanent brain damage (which you might expect after being infected by a parasite that eats your nervous system). Is there any silver lining? Yes!

Naegleriasis is extremely rare – globally, only around 300 cases have been recorded in the five decades since 1965. By contrast, almost as many people drowned in Australia between 2016 and 2017. So long as you avoid shooting unchlorinated water up your nose-holes, and take a noseclip on your next lake swim, the chance of infection is next to none.

This isn’t Night of the Living Dead. Hungry amoebae aren’t about to break into your bedroom and eat you alive. But if you’re ever tempted to cool off in a suspicious-looking pond, think twice about inviting the zombie apocalypse into your nose.